The instant invention relates to thermostatic switches, and more particularly to a thermostatic switch which has improved responsiveness to energy transferred via convection.
In certain applications, it can be important for thermostatic switches to be operative with relatively short response times to enable them to rapidly open or close circuits connected thereto in response to temperature changes in their surrounding environments. For example, thermostatic switches which are utilized for protecting various machinery and electronic equipment against over heating must generally be highly responsive to ambient temperature conditions in order to prevent damage to the machinery or equipment with which they are associated. Generally, heretofore, conventional bimetallic disc-actuated thermostatic switches have been utilized for applications of this type; although they have not always been entirely satisfactory for applications which have required extremely high responsiveness to ambient conditions. In this regard, the response times of bimetallic disc-actuated thermostatic switches are generally directly related to the abilities of the bimetallic discs thereof to rapidly absorb energy from their surrounding environments. While in many applications the abilities of the bimetallic discs of thermostatic switches to absorb energy via radiation or conduction are of main importance, in other applications the abilities of the bimetallic discs of switches to absorb energy through convection are of primary importance. However, heretofore, most thermostatic switches have been constructed so that the bimetallic discs thereof are fully enclosed in cap assemblies or housings so that they are not directly exposed to ambient air. Accordingly, the bimetallic discs of most of the heretofore available thermostatic switches have only been indirectly responsive to energy transferred via convection through the caps or housings thereof. Further, while a limited number of bimetallic disc-actuated thermostatic switches have been heretofore available which have included partially exposed bimetallic discs for directly receiving energy via radiation and convection, such switches have only been adapted to enable the bimetallic discs thereof to receive energy through the outwardly facing outer surfaces thereof.
The instant invention provides an effective thermostatic switch which is operative with increased responsiveness to energy transferred via convection. Specifically, the instant invention provides a bimetallic disc-actuated thermostatic switch which, in its preferred form, is constructed so that both the inwardly facing and outwardly facing sides of the bimetallic disc thereof are exposed to the surrounding air for receiving energy via convection. More specifically, the thermostatic switch of the instant invention comprises a basic switching assembly of generally conventional construction and an improved cap and disc assembly on the switching assembly which is adapted to provide increased responsiveness to energy transferred via convection. Still more specifically, the basic switch assembly of the switch of the subject invention comprises a housing, a fixed and movable contacts in the housing, and the cap and disc assembly comprises a bimetallic disc, means supporting the bimetallic disc adjacent one end of the housing, and a retainer cap for retaining the disc on the support means. The switch is further constructed so that the movable contact is movable between engaged and disengaged positions relative to the fixed contact, and the bimetallic disc is of conventional construction and adapted so that it is responsive to a predetermined temperature for movement between actuated and unactuated positions thereof, and the basic switch assembly further comprises means effecting communication between the disc and the movable contact so that the movable contact is moved between the engaged and disengaged positions thereof when the disc is moved between the actuated and unactuated positions thereof. The retainer cap is constructed so that it includes a sidewall portion having an outer end and retainer means on the outer end for retaining the disc on the support means. The retainer cap is further constructed so that it includes at least one air circulation opening in the sidewall portion thereof for effecting communication between the exterior of the retainer cap and the underside of the bimetallic disc, and it is preferably of circular configuration and assembled on the housing so that the bimetallic disc is positioned adjacent the outer end of the sidewall portion of the retainer cap. The retainer cap preferably includes a plurality of air circulation openings therein which are formed as elongated slots extending around at least approximately 80% of the circumference of the cap adjacent the outer end of the sidewall portion. The support means for supporting the bimetallic disc preferably comprises a plurality of spaced support elements which are operative for supporting the disc at a plurality of spaced points adjacent the periphery of the disc so that the underside of the disc communicates with the exterior of the cap through the open areas between the support elements of the support means and through the openings in the sidewall portion of the cap. The retainer means on the retainer cap preferably comprises a substantially circular end wall having an enlarged aperture therein, and it is assembled so that the end wall operates to retain the peripheral portions of the bimetallic disc but so that the central portion of the disc is free to flex and is exposed through the enlarged aperture in the end wall.
It has been found that as a result of the above features, the thermostatic switch of the instant invention is operative with increased responsiveness to ambient conditions by means of energy transferred via convection. Specifically, it has been found that the retainer cap and the support means provide effective direct communication between the ambient air and the inwardly facing underside of the bimetallic disc of the switch in order to increase the amount of heat which is transferred to the disc from the ambient air. The retainer means portion of the cap further increases the responsiveness of the disc to ambient conditions by providing direct communication between the outwardly facing side of the disc and the ambient air.
Accordingly, it is a primary object of the instant invention to provide a thermostatic switch which has improved responsiveness to energy transferred via convection.
Anther object of the instant invention is to provide a bimetallic disc-actuated thermostatic switch wherein direct communication is provided between the underside of the bimetallic disc thereof and the ambient air.
An even further object of the instant invention is to provide a bimetallic disc-actuated thermostatic switch wherein direct communication is provided between both sides of the bimetallic disc thereof and the ambient air.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.